1. Field
The present disclosure relates to a rotor of a rotary electric machine and a method of producing a rotor of a rotary electric machine.
2. Description of the Related Art
Widely known rotors used in rotary electric machines include a rotor core including magnetic steel sheets stacked on one another (see FIG. 13 and FIG. 14, or Japanese Patent No. 5118920, for example).
As illustrated in FIG. 13, a rotor 100 of a widely known rotary electric machine includes a rotor core 105 including steel plates 101 stacked on one another, permanent magnets, and a rotor shaft. The permanent magnets and the rotor shaft are not illustrated. The rotor core 105 has magnet insertion holes 103 arranged at first circumferential intervals (45° intervals, for example). The permanent magnets are disposed in the magnet insertion holes 103. The rotor shaft is disposed in a shaft hole 107 positioned in the middle of the rotor core 105.
As illustrated in FIG. 14, the steel plates 101 included in the rotor core 105 each have magnet insertion hole pieces 103a and through hole pieces 109a. The magnet insertion hole pieces 103a are arranged at the first circumferential intervals in the circumferential direction. The through hole pieces 109a, which extend through the steel plate 101 in the axial direction, are positioned inward from the magnet insertion hole pieces 103a and arranged at second circumferential intervals (45° intervals, for example).
In the steel plate 101, an inner annular section 111a positioned radially inward from the through hole pieces 109a and an outer annular section 113a positioned radially outward from the through hole pieces 109a are connected through ribs 115 positioned between the through hole pieces 109a. 
The steel plates 101 having the same configuration are stacked in the axial direction so as to constitute the rotor core 105 having the magnetic insertion holes 103, which are provided by the magnetic insertion hole pieces 103a in the steel plates 101, the through holes 109, which are provided by the through hole pieces 109a in the steel plates 101, and rotor core inner and outer sections 111 and 113, respectively, which are provided by the inner annular section 111a and the outer annular section 113a of the steel plates 101. In other words, the rotor core 105 looks like an extension of the steel plate 101 elongated in the stacking direction (axial direction).
During the production of the rotor core 105, every predetermined number of the steel plates 101 (ten, for example) may be rotated by an angle corresponding to the first circumferential interval so as to reduce the accumulated thickness deviation due to the stacking of the steel plates 101. In such a case, the through hole pieces 109a in axially adjacent steel plates 101 overlap each other when viewed in the axial direction, since the first and second circumferential interval are the same in the steel plates 101. Thus, the rotor core 105 looks like an extension of the steel plate 101 elongated in the stacking direction (axial direction).
In such a rotor core 105, the ribs 115 of the stacked steel plates 101 overlap each other when viewed in the axial direction. Thus, stress concentrates on an inner connecting section 117 between the rib 115 and the inner annular section 111a (rotor core inner section 111). The inner annular section 111a (rotor core inner section 111) and the rotor shaft inserted into the shaft hole 107 needs to have a locally-increased thickness at circumferential portions corresponding to the inner connecting section 117 such that the rotor core 105 has sufficient strength. Practically, an increase in the overall thickness of the inner annular section 111a (rotor core inner section 111) and an increase in the overall thickness of the rotor shaft are required.
The through hole 109 looks like an extension of the through hole piece 109a elongated in the axial direction. If the rotor 100 is used in the presence of oil (liquid cooling), the oil may enter the through hole 109 through spaces between the stacked steel plates 101, for example. In such a case, the oil may accumulate in one of the through holes 109. The accumulation of the oil in one of the through holes 109 may lead to eccentricity (imbalance) of the rotor 100. This may increase vibrations and noise during the rotation, deteriorating the quality of the rotor.
To solve the above-described problems, the rotor of the rotary electric machine disclosed in Japanese Patent No. 5118920 may be used. The rotor of the rotary electric machine disclosed in Japanese Patent No. 5118920 includes a rotor core which is fixed to the rotor shaft and has refrigerant passages. The rotor core includes first plates and second plates stacked on one another in the axial direction.
The first plate has first holes, which constitute the refrigerant passages, and a first rotation stopper configured to be fitted to the rotor shaft so as to prevent the first plate from rotating with respect to the rotor shaft. The second plate has second holes, which constitute the refrigerant passages, at positions displaced from the first holes in the circumferential direction, and a second rotation stopper configured to be fitted to the rotor shaft so as to prevent the second plate from rotating with respect to the rotor shaft.
When the first plate and the second plate are stacked in the axial direction, the first holes and the second holes, which are displaced from each other in the circumferential direction, are in communication with each other. In addition, the first and second holes overlapping each other constitute a hole extending around the rotor shaft in the circumferential direction as a whole. This configuration enables a refrigerant medium to be supplied evenly to the rotor core in the circumferential direction. In addition, since the ribs between the circumferentially adjacent first holes and the ribs between the circumferentially adjacent second holes are displaced from each other in the circumferential direction, stress does not concentrate on a base of each rib.